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opfromthestart
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Identification of a mystery metal
My AP Chemistry teacher recently found a sample of a "silver unknown metal"(written on the container) with a label of 8.19 g/cm^3. I have tested its
reactivity with water and dilute sulfuric acid and it seems to be relatively unreactive. Me and one of my classmates think that it may be an alloy of
nickel, chromium, cobalt, iron, and beryllium(possibly not all of them, but all could be possibilities). What tests could be easily done in a high
school lab that could possibly confirm the identity of the metal as nickel or something else?
On a slightly related note, is there any database or other resource for the rate laws and constants for single and double replacement reactions for
metals?
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j_sum1
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First question: do you know whether it is a relatively pure metal or an alloy?
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DraconicAcid
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Does it react with more concentrated hydrochloric acid? Is it magnetic?
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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fusso
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What about conc HNO3? Aqua regia? Bleach? (some PGMs react with bleach)
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elementcollector1
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Have you verified that density? I don't doubt it, but it's always good to check.
If that density is accurate, the only pure element that would be reasonably close would be terbium (d = 8.23 g/cc). This is disproven in that it does
not react with water or dilute sulfuric acid, two things which would easily provoke a rare earth into producing hydrogen. So it must be an alloy.
Magnetism would be an easy check for a ferrous alloy, with the caveat that some stainless steels are nonmagnetic due to Ni content. Nickel would also
explain non-reactivity, and the range of density for stainless steel does include the density of your mystery metal (nickel being 8.9 g/cc, iron being
7.87 g/cc and chromium being 7.19 g/cc).
Maybe we could also get a photo of this mysterious sample?
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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diddi
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if the density is very accurate, this might help
https://www.engineeringtoolbox.com/metal-alloys-densities-d_...
Beginning construction of periodic table display
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ScienceHideout
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Is this an actual case of AP Chem Teacher finds mystery metal, or is he/she fabricating this story to test your practical skills?
Either way, there are a lot of fun ways to find out. Obviously, I would re-check that density just to make sure it is 100% accurate and compare to the
table from Diddi above. Excellent preliminary step.
I would avoid destructive chemical techniques at all costs. Corrosive acids are a bitch to use, it creates nasty fumes which are probably a bit too
dangerous to make in typical AP chem labs, and you risk destroying your sample... which you especially don't want to do if it is of any value (always
possible!). Any professional analytical chemist would just do some XRF analysis to confirm its identity, which is non-destructive, and if the chemist
didn't have access to an XRF spectrometer, he or she still likely has the ability to analyze less than a milligram of sample with some ICP instrument.
Since most AP Chem labs are not equipped to do such microscale analysis of such things, you should first rely on cheap and time-tested non-destructive
techniques. Once again, test the density over again. Touch a magnet to see if it sticks. Another possibility is calorimetry. Submerge the sample in
boiling hot water for several minutes, take it out and drop it into a well-insulated cup of water, and monitor how the temp increases. 
If you've exhausted all options, and you must do destructive analysis, see if you can cut or snap off a tiny piece- half of a gram or so- to dissolve
and then do chemical tests!
hey, if you are reading this, I can't U2U, but you are always welcome to send me an email!
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j_sum1
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Further to the magnetism tests:
Test for ferromagnetism by touching a magnet on one side and seeing if you can get coarse iron filings to stick to the other. See if they fall off
once the magnet is removed. (Just to eliminate electrostatic and other kinds of attraction.)
Drop it on a piece of polystyrene so that it floats in a dish of water. Even if it is not ferromagnetic you can distinguish whether it is
paramagnetic or diamagnetic by putting a strong magnet in close proximity.
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Sulaiman
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A flame test may reveal something https://en.wikipedia.org/wiki/Flame_test
a spark spectrum is probably (I've not personally tried) do-able https://en.wikipedia.org/wiki/Atomic_emission_spectroscopy
CAUTION : Hobby Chemist, not Professional or even Amateur
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opfromthestart
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I do not but since it does not fit the density or reactivity of any pure metals I assume it is an alloy.
I do not know for either of these, I will try to test magnetism at least fairly soon.
I will try nitric acid but for reasons of safety she is hesitant to use aqua regia. I'll also see if I can try bleach but I doubt it is a PGM, since
their densities are significantly higher than the density on the label.
Quote: Originally posted by elementcollector1  | Have you verified that density? I don't doubt it, but it's always good to check.
If that density is accurate, the only pure element that would be reasonably close would be terbium (d = 8.23 g/cc). This is disproven in that it does
not react with water or dilute sulfuric acid, two things which would easily provoke a rare earth into producing hydrogen. So it must be an alloy.
Magnetism would be an easy check for a ferrous alloy, with the caveat that some stainless steels are nonmagnetic due to Ni content. Nickel would also
explain non-reactivity, and the range of density for stainless steel does include the density of your mystery metal (nickel being 8.9 g/cc, iron being
7.87 g/cc and chromium being 7.19 g/cc).
Maybe we could also get a photo of this mysterious sample? |
The first metal my chem teacher thought it would be was terbium, hence my tests with water and dilute acid since it would react even with that. I will
have to test for stainless steel also but I doubt it because I was able to scrape some of the metal off with a scoopula fairly easily.
I will try to get a photo later today.
| Quote: Originally posted by ScienceHideout | Is this an actual case of AP Chem Teacher finds mystery metal, or is he/she fabricating this story to test your practical skills?
Either way, there are a lot of fun ways to find out. Obviously, I would re-check that density just to make sure it is 100% accurate and compare to the
table from Diddi above. Excellent preliminary step.
I would avoid destructive chemical techniques at all costs. Corrosive acids are a bitch to use, it creates nasty fumes which are probably a bit too
dangerous to make in typical AP chem labs, and you risk destroying your sample... which you especially don't want to do if it is of any value (always
possible!). Any professional analytical chemist would just do some XRF analysis to confirm its identity, which is non-destructive, and if the chemist
didn't have access to an XRF spectrometer, he or she still likely has the ability to analyze less than a milligram of sample with some ICP instrument.
Since most AP Chem labs are not equipped to do such microscale analysis of such things, you should first rely on cheap and time-tested non-destructive
techniques. Once again, test the density over again. Touch a magnet to see if it sticks. Another possibility is calorimetry. Submerge the sample in
boiling hot water for several minutes, take it out and drop it into a well-insulated cup of water, and monitor how the temp increases.
If you've exhausted all options, and you must do destructive analysis, see if you can cut or snap off a tiny piece- half of a gram or so- to dissolve
and then do chemical tests!
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I believe that she doesn't actually know what the metal is. She inherited it from a teacher from the 70's and it was labeled as lead. She calculated
the density herself so that is confirmed.
I didn't think to test the specific heat but I will attempt to test that and report what I get.
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opfromthestart
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These are pictures of the container and the metal itself. The blue label was put on by my chem teacher.
The damage to the leftmost rod is from a scraping I took to test it against sulfuric acid.
 
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opfromthestart
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The physics teacher tested it's magnetism with a neodymium magnet and it was not magnetic(or at least ferromagnetic). I will still have to see if it
reacts to a magnet when floating on Styrofoam or if iron filings stick to it when it is against a magnet.
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Ubya
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If you were able to scrape it easily it's not SS.
To know exactly what alloy is you must do some wet chemistry (destructive).
Scrape some of it or cut a little piece, you need way less than a gram.
Dissolve it in a few drops of nitric acid (if your teacher thinks you can't do it let her do it), if it doesn't dissolve in cold acid heat it in a
water bath (a beaker filled with water on a hot plate).
Notice the color. Any blue or green can indicate copper, nickel, chromium or vanadium, red Cobalt, yellow iron. add HCl to precipitate insoluble AgCl2
and PbCl2(if present), filter or centrifuge. To the supernatant add H2S or Na2S. Bismuth, cadmium, copper and tin sulfides will precipitate. Cadmium
sulphide is yellow.
Filter or centrifuge. To the supernatant add ammonia to get pH 10, add again H2S and precipitate nickel, zinc, Cobalt and manganese sulfide. Zinc
sulfide is white while manganese sulfide is pinkish.
Then it's a matter of seeing what you get and use other tests to check
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fusso
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| Quote: Originally posted by opfromthestart | | The first metal my chem teacher thought it would be was terbium, hence my tests with water and dilute acid since it would react even with that. I will
have to test for stainless steel also but I doubt it because I was able to scrape some of the metal off with a scoopula fairly easily.
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This confirms the metal is quite soft. Can you bend it easily? Or hammering it to test malleability? Melting
point test?
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DraconicAcid
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| Quote: Originally posted by Ubya | If you were able to scrape it easily it's not SS.
To know exactly what alloy is you must do some wet chemistry (destructive).
Scrape some of it or cut a little piece, you need way less than a gram.
Dissolve it in a few drops of nitric acid (if your teacher thinks you can't do it let her do it), if it doesn't dissolve in cold acid heat it in a
water bath (a beaker filled with water on a hot plate).
Notice the color. Any blue or green can indicate copper, nickel, chromium or vanadium, red Cobalt, yellow iron. add HCl to precipitate insoluble AgCl2
and PbCl2(if present), filter or centrifuge. To the supernatant add H2S or Na2S. Bismuth, cadmium, copper and tin sulfides will precipitate. Cadmium
sulphide is yellow.
Filter or centrifuge. To the supernatant add ammonia to get pH 10, add again H2S and precipitate nickel, zinc, Cobalt and manganese sulfide. Zinc
sulfide is white while manganese sulfide is pinkish.
Then it's a matter of seeing what you get and use other tests to check
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Wet chemistry with sulphides isn't going to happen in a high school lab.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Ubya
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Thioacetamide could be used to generate S-- in situ, to not have to deal with gaseous H2S or a generator
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opfromthestart
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Why couldn't it? As part of the class we have already used Na2S in a One Pot Silver demonstration. The lab also has a fume hood so if
H2S fumes are the problem that could be worked around.
[Edited on 5-1-2019 by opfromthestart]
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DraconicAcid
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That surprises me, just from the toxicity of H2S.
At any rate, the colour of the sulphide isn't very characteristic, because small amounts of impurities can turn a white or pink precipitate an ugly
brown.
Hmmm...if it's soft enough to be scraped with a spatula, my first guess would be tin, or an alloy of tin (a form of solder?). If it dissolves in HCl
to give a colourless solution, that would support that hypothesis. If it gives a white precipitate while doing so, that would probably be some lead
chloride (so you had an alloy).
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Ubya
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Most sulphides are black, so even a brown color can be helpful.
I hope the alloy to be a mix of just 2 or 3 metals, one being tin or lead given the softness.
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Metacelsus
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That looks exactly like some Wood's alloy from the lab I worked in back at the University of Minnesota. The type of container is even the same. (I
used it as a bath for a high-temperature reaction.)
The density of Wood's alloy is 9.67 g/mL, so it's probably not that. But I would check the melting point to see if it's something similar. Perhaps
Field's alloy?
edit: Field's alloy is 7.88 g/mL. Maybe it's a slightly woody field? I'll call it "savanna" alloy
[Edited on 2019-5-1 by Metacelsus]
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Sulaiman
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Tin:Lead solder looks likely, density close to eutectic mixture.
P.S. just got in from my lab - been melting lead and tin so probably biased.
[Edited on 1-5-2019 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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fusso
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I now wonder, if it's some kind of fusible alloy...
try putting it in boiling water to see if it melts?
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ScienceHideout
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Visually, I'm inclined to believe it's tin. I know that tin comes in sticks very similar to that. A lot of people have said this, but I'll say it
again. Before doing anything else, measure the density again. There is always the possibility that whoever wrote that on the bottle did it wrong.
EDIT: Also, looking at the bottle, it is probably a single metal and not an alloy. It has an analysis on it that says 100.0%...
[Edited on 2-5-2019 by ScienceHideout]
hey, if you are reading this, I can't U2U, but you are always welcome to send me an email!
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happyfooddance
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Hehe.
Did no one else think this was funny? Thanks, Mc
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Metacelsus
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Good catch! I didn't notice that.
You should definitely check the density again, as other commenters have suggested.
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